Material for selectively controlling metal-pickling baths



i lu n m Patented Mar. 17, 1931 UNITED STATES PATENT OFFICE JAMES H. GBAVELL AND ALFRED DOUTY, F ELKINS PARK, PENNSYLVANIA; SAID GBAVELL ASSIGNOR TO AMERICAN CHEMICAL PAINT COMPANY, OF AMBLER, PENN- SYL'VAN IA, A CORPORATION OF DELAWARE MATERIAL EOR SELECTIVELY CONTROLLING METAL-PICKLING BATES No Drawing.

This invention relates broadly to the art of pickling and specifically to selectively controlling the action of pickling baths.

The objects of the invention are to save acid, to save metal, to minimize the escape of abnoxious fumes, to avoid discoloration of the work, to prevent overpickling, to prolong the life of pickling baths, to save time,

t to conserve health, and to generally improve the art of pickling.

We have practiced pickling according'to the method described in U. S. Patent No. 288,150 and we have noted that the results are beneficial, but there are numerous disad- I5 vantages which limit the utility of that method. We have found that the addition of p0; tassium cyanide to the pickling baths not only prevents acid brittlenesghnt also tends aw in that n tect eat extent a 'ainst the GM But to oifset these advantages, the work is discolored poisonous gas escapes from the bath and the desirable action of the potassium cyanide is not lasting.

It occured to us that an improvement might be effected by adding the potassium cyanide in small increments and although this prolonged the life of the cyanide it did not overcome the discoloration of the work or the escape of poisonous fumes.

We have discovered that if we replaced the potassium cyanide by a substance that would react wi th a developed by the reaction between the acid bath and the metal being pickled, to liberate hydrocyanic acid within the bath, new and surprising results were obtained, the bath ceased to stain the work or to liberate a noticeable or objectionable amount of poisonous fumes,

and a very small quantity of the added substance produced a powerful and lasting effect in selectively controlling the bath, in that after the oxide or scale was removed from the work, the corrosive effect of the bath on the work was materially reduced or checked.

Based on our discovery, we have invented a commercial process and a pickling adjunct which we will now describe.

Application filed March 29, 1927. Serial No. 179,388.

We have found, as a class, that the thiccyanatesreact well with nascent hydrogefi tFfiiriiish-hydrocyanic acid within the pickling bath. Among these we prefer to use ammonium thiocyanate due to its co rcial availability. V I v I In one way of practicing our invention, we f,

gallons 50.00 gallons .50 pounds This bath we maintain at a temperature of 180 F. more or less. When the steel to be J5 cleaned is introduced into this bath, the scale is quickly removed, after which the action of the bath is automatically checked or reduced to such an extent that even if the cleaned work is allowed to-remain in the" bath for'a long period it shows no ill effects.

Although the corrosive action of the acid on the metal is materially reduced, it is not stopped altogether and consequently hydrogen still escapes from the bath. The hydro- 7 gen rises to thesurface of the bath forming unstable bubbles which break and throw a spray of acid bath into the air to the great detriment of health and materials in the vicinity. In order to overcome this disadvantage we may add, in addition to thiocyanate, a foaming agent.

We have investigated the compatibility of the various foaming agents and thiocyanate and find that they are not only compatible but that the selective controlling effect is improved by the simultaneous use of these dissimilar classes of materials. Although rye meal liquor, saponin, and the like may be used to advantage, we prefer to use cellulose pulp waste liquor. This we may add to the bath as follows Water 1000.00 gallons Sulphuric acid (66) 50.00 gallons Ammonium thiocyanate 1.00 pound Cellulose pulp waste liquor..- .50 gallons The foaming agent makes the bubbles produced on the surface of the bath stable, with the result that the bath covers itself with a twig:

Emma" may euse 1n n ven 1011 but Cellulose pulp waste liquor .50 gallons 7 Ammionium thiocyanate 1.00 pound r;

This forms about one half gallon of our admixture which is sufiicient for treating a bath of the size given above.

If the admixture is to be transported, it is more convenient, if it is prepared in the dry state. In that case we select a dry foaming '20 'agent, like saponin or evaporated cellulose pulp liquor, and proportion them as fol- 'lows:

Evaporated cellulose pulp waste liquor 2.00 pounds Ammonium thiocyanate 1.00 pound It should be noted that although we have specified certain'quantities of the ingredients in relation to the size of the pickling solution, the proportions of water, acid, control material and foaming agent may be varied ,through a great range without deviating from the spirit of this invention, as the effect pro- 'duccd by each ingredient may be inchnsed of diminished by varying its concentration, as

individual tastes will dictate.

W have foud that not onl huric acid chlorio o q l o sphp c ag d ma also be u d,

' "40 but as sulp uric acid is in more ge era use for the purpose of pickling, we have deascribed our invention in connection with that acid. 7

- Weclaim: v i

{Y 1. A pickling bath for metal comprising an 4 admixture of water, acid and a thiocyanate. 2. A pickling bath for metal comprising an admixture of water, acid, and ammomum thiocyanate.

+5 JALLES H. GRAVELL. I ALFRED DOUTY. 

